The present invention relates to a process for producing a planar optical waveguide for guiding light with defined polarisation, by depositing, on a substrate, thin, vitreous layers from the gas phase in accordance with a scheme which enables a given refractive index profile of the layers to be produced, thereby forming a light-guiding core region and cladding layers adjoining said core region, light-guiding strips subsequently being produced from these layers by masking and etching away the unmasked regions.
Planar single-mode optical waveguides for guiding light with defined polarisation have important applications as the basic module in integrated optical arrangements for sensor systems and for single-mode fibre communications, especially for transmitting coherent light with a preferred plane of polarisation. One specific example where such optical waveguides are used is the gyroscope.
Until now, waveguides chiefly constructed from LiNbO.sub.3 crystals (lithium niobate) have been used in the manufacture of planar single-mode optical waveguides, which can conduct light with defined polarisation (polarisation-receiving or polarising optical waveguides), the light-guiding core of said crystals having been produced by diffusion of titanium into a channel formed in a LiNbO.sub.3 crystal and by the exchange of protons over a short stretch of the light-guiding region of Li.sup.+ for H.sup.+ (Electronic Letters, Feb. 1984, Vol. 20, No. 3, p. 128). The principle of operation of such integrated optical polarisers relies on the fact that the refractive indices of the LiNbO.sub.3 crystal making up the cladding of the optical waveguide differ in the direction of the various crystal axes (birefringence).
Polarising or polarisation-receiving single-mode optical fibres are also produced by stress-induced birefringence. This stress-induced birefringence is caused by the action of different compressive and/or tensile stresses on the core of the single-mode waveguide from opposite directions, and is responsible for the fact that in single-mode waveguides the two mutually perpendicular propagation modes (planes of polarisation) do not become coupled together.
The foregoing optical waveguides, embedded in a LiNbO.sub.3 crystal have various more or less serious disadvantages:
(a) the crystalline structure of the LiNbO.sub.3 determines the direction of the preferred polarisation; as a result of this, waveguide curvatures can alter or even completely nullify the birefringence; this severely limits the potential usable region; PA0 (b) the transmitted light undergoes relatively great attenuation; PA0 (c) the relatively great difference in the refractive index between the LiNbO.sub.3 crystal and the light-conducting single-mode waveguide to be coupled thereto causes problems in fibre coupling, in particular high reflection at the interface of the LiNbO.sub.3 crystal and the optical waveguide, as well as poor field adaptation; PA0 (d) one particularly serious disadvantage is the fact that the material constants rigidly determine the birefringence; PA0 (e) the method for producing integrated optical polarisers of this type is very costly and laborious.